Why does Resharper say, “Co-variant array conversion from string[] to object[] can cause run-time exception on write operation” with this code? [duplicate]

The method comboBoxMonth.Items.AddRange expects an object[] parameter. months.ToArray() is string[]. A cast from string[] to object[] is valid, but if the method tries to modify elements of the array, you will get run-time errors. In this case it doesn’t, so you can ignore the warning.

If it annoys you, you can use ToArray<object>()

comboBoxMonth.Items.AddRange(UsageRptConstsAndUtils.months.ToArray<object>());

It will return object[] and no cast will be needed.